1. Field of the Invention
The present invention relates to an electric rotary shaver that includes an inner cutter that rotates while making sliding contact with the inner surface of a substantially circular disk form outer cutter that has a plurality of openings formed on the top surface.
2. Prior Art
In a typical electric rotary shaver, numerous small hair entry openings (e.g., slits) are formed in the top surface of a substantially circular disk form outer cutter that has in its inside a circular track (groove), and an inner cutter is provided so that it rotates while causing its blades (cutter blades) that are integrally disposed on this inner cutter to make sliding contact with the inner surface of this outer cutter. Such an electric rotary shaver is disclosed in, for instance, Japanese Patent Application Laid-Open (Kokai) No. 06-238070.
More specifically, in the conventional inner cutter disclosed in the above prior art, an inner cutter main body made of metal is fastened to a boss that is made of a synthetic resin.
FIG. 10 is a perspective view of the inner cutter disclosed in the above-identified prior art. FIG. 11 is a perspective view of the outer cutter that is used with this inner cutter 10. FIG. 12 is a side view of the inner cutter with a part of the inner cutter omitted. FIG. 13 is a partially sectional side view of this inner cutter. FIG. 14 is a cross sectional side view of an assembled inner cutter and outer cutter of the prior art.
The outer cutter 12 is, as seen from FIG. 11, made of metal and in a substantially circular disk shape. In other words, this outer cutter 12 is made so that a circular plate is bent at the circumferential edge so as to have a shallow substantially dish-form shape or substantially inverted dish-form shape, numerous small hair entry openings constituting slits 14 are formed in this outer cutter 12 in a radial pattern, and an annular groove 16 is further formed in this outer cutter. This groove 16 extends across the slits 14 in the vicinity of the midpoint of each slit 14. As a result, the outer cutter 12 has two annular sections (or annular tracks) 12A and 12B (see FIG. 14) on either side of this groove 16. A structure in an outer cutter that has such two tracks 12A and 12B is called a double track structure.
The boss 18 (see FIG. 10) of the inner cutter 10 is made of a POM (polyoxymethylene) resin, e.g., “Delrin” (Registered Trademark), a product of DuPont, etc.; and the lower portion of the boss 18 has an inverted dish form portion that opens at the bottom. As seen from FIG. 12, an engaging hole 22 with which a rotary shaft (not shown in the drawings) of the shaver is engaged from below is formed in this inverted dish form portion 20. A columnar center projection 24 is disposed in the center of the upper surface of the boss 18.
The inner cutter main body 26 (see FIG. 10) is obtained by stamping and bending a metal plate, and it has a substantially pinwheel-form shape. More specifically, the inner cutter main body 26 has ten mutually separated raised portions 30, which are raised from the outer circumference of a circular plate portion 28, and blade portions 32, which are formed by further bending the raised portions 30 in the radial direction of the boss 18. The center projection 24 of the boss 18 passes through the center of the circular plate portion 28 and is securely fastened by hot-crimping to the upper surface of the inverted dish form portion 20 of the boss 18.
The upper portion of each one of the blade portions 32 of the inner cutter main body 26 is formed into a bifurcated shape, and the ends of the bifurcated blade portions respectively form cutter blades 34. The two cutter blades 34 are respectively set from below (i.e., from the inside) in the two annular sections 12A and 12B of the double-track outer cutter 12. Accordingly, when the inner cutter 10 comprising substantially the boss 18 and inner cutter main body 26 is rotated by the rotary shaft (not shown in the drawings) connected to the motor installed in the shaver main body (not shown in the drawings), the cutter blades 34 run while being in contact with the inner surfaces 12a and 12b of the annular sections 12A and 12B of the outer cutter 12 (see FIG. 14). As a result, hair (whiskers, etc.) entering through the slits 14 of the outer cutter 12 is cut by the cutter blades 34 of the rotating inner cutter 11.
The upper end portions of the cutter blades 34 of the inner cutter 10 shown here are inclined so that these upper end portions are offset further in the direction of rotation of the inner cutter 10 than the lower portions of the blade portions 32. In other words, the upper end portions are inclined toward the front in terms of the rotating direction of the inner cutter 10.
Furthermore, as shown in FIGS. 12 and 13, recesses 36 are formed in the surfaces of the respective cutter blades 34 so that the recesses 36 face the counter-rotation direction, so that a part of each of the recesses 36 reaches the upper end surface (i.e., the cutting surface that makes sliding contact with the inner surface of the outer cutter 12) of the each cutter blades 34. These recesses 36 prevent shaving debris and dirt from adhering to the cutter blades 34, and it also functions to decrease the area of contact between the cutter blades 34 and the outer cutter 12, reducing the driving resistance (see the above-described cited prior art). In the present invention, however, the recess 36 can be omitted.
The above-described inner cutter 10 and outer cutter 12 make a pair; and, for instance, three pairs of such cutters are provided at the vertices of an equilateral triangle in the cutter head of a shaver. Three inner cutters 10 are rotationally driven by a motor installed in the main body of the shaver. A shaver with two pairs of inner and outer cutters and a shaver with only a single pair of such cutters are also possible.
As seen from the above, in the conventional inner cutter, the entire inner cutter main body 26 is made by press-stamping a single metal plate and then bending this plate approximately 90° at the two places A and B as shown in FIGS. 12 and 13 and 14. When the number of locations where such bending is performed is thus large, the distance from the center of the inner cutter 10 to the cutter blades 34, especially the distance to the inner circumferential edges and outer circumferential edges of the cutter blades 34, tends to become non-uniform, resulting in that the inner and outer circumferential edges of the cutter blades 34 contact the inner and outer circumferential walls 12c and 12d and the inner and outer circumferential walls 12e and 12f of the respective annular sections 12A and 12B of the outer cutter 2. This leads to problems such as an aggravation of operating noise and deterioration in sharpness due to an expansion of the annular sections' width of the outer cutter 12. Furthermore, it is necessary, for making inner cutters, to use a special metal material that has good pressing characteristics and that can be hardened.
Furthermore, in rotary shavers, a frictional resistance force generated by the sliding motion between the cutter blades 34 of the inner and the outer cutter 12 and a resistance force that generates when hair is cut are applied to the cutter blades 34. Accordingly, the inner cutter main body 26 must have a sufficient thickness and a high rigidity so that the cutter blades 34 do not vibrate by such resistance forces. Ordinarily, an SUS420J2 metal plate with a thickness of 0.5 mm is used for inner cutters of rotary shavers. In cases where such a thick metal material is pressed (subjected to stamping and bending), the working precision tends to be poor, and problems such as the occurrence of vibration, increase in operating noise, deterioration of sound quality and deterioration of sharpness due to biased wear of the cutter blades tend to occur.
In order to increase the working precision, it is desirable to make the length of the bent portions (A, B) formed by pressing as small as possible. However, if the length of these portions is shortened, the width of the raised portions 30 is naturally reduced, which is disadvantageous from the standpoint of preventing vibration of the cutter blades 34. If the distance between the tip end portions of the cutter blades 34 to which a resistance force is applied and the bent portions (A, B) is large, the stress applied to the bent portions (A, B) increases; and this is disadvantageous from the standpoint of vibration. However, in inner cutters having the conventional structure, there are limitations in shortening this distance.
Thus, because of the structural problems such as poor pressing precision, a large number of bent portions and the like, problems such as vibrations in the cutter blades, resonance of various parts, an increase in operating noise and a deterioration in sound quality have been unavoidable.